1. Field of the Invention
The invention relates to presses and, in particular, to gap-framed type presses. More particularly, the invention relates to a gap-framed press in which the lower die holding bed and vertical side frame members are interconnected by spherical bearings. The elastic bending and deformation exerted on the press frame during a press operation are transmitted through the bearings to the various frame and die holding components so that the top and bottom dies move in unison in the same direction to maintain the dies in parallel and reduce die wear and breakage.
2. Description of the Prior Art
There are numerous types and styles of presses for performing metal-working procedures such as bending, shaping, punching or shearing on a workpiece. In many presses, a pair of upper and lower die members are moved into cooperating relationship with each other by power-driven means such as hydraulic or mechanically actuated devices or the like. The lower die usually is mounted on a stationary bed and the upper die is mounted on a vertically movable ram or slide. Large forces are exerted on the press frame and components thereof when the dies are brought into engagement with each other during the metal-working operation.
There are various types of presses classified according to frame design. Two general types of presses are referred to as being gap-framed and straight-sided. A straight-sided press has a slide or ram which holds a top die. The ram travels downwardly between two straight sides of a housing usually supported by four corner posts to perform work on the workpiece which is supported on a bottom die mounted on the stationary press bed. A gap-framed press has side frames which form the general shape of the letter "C". This shape permits feeding of wide or large sheets from both sides and from the front of the press into the work area between the dies. Also, these gap-framed presses enable a workman to be closer to the workpiece than possible with the straight-sided press frame constructions. Furthermore, the gap-framed presses are smaller and less expensive than a comparable straight-sided press.
Although the gap-framed type presses have many advantages over the straight-sided presses, they have the disadvantage of misalignment occurring between the upper and lower dies due to the unbalanced forces which are exerted on the C-shaped press frame side members during a press operation. During a press operation, the forces exerted on the C-shaped frame will cause the upper portion of the frame sides to rotate or tilt in one direction causing the upper die to rotate or tilt in the same direction. This results in misalignment with the lower die which may not move as much as the upper die or may move in an opposite direction. Even though such misalignment is relatively slight (thousandths of an inch), it results in uneven die wear and breakage, especially when the dies include components such as pins on one die which move into and out of openings formed in the opposite die. This misalignment problem is further magnified in high-speed press operations wherein large numbers of parts are produced in a relatively short period of time. The vertical side frame members of a gap-framed press also will tend to move inwardly toward each other and then outwardly due to the repeated flexing up and down of the press bed and top ram. Again, even though this flexing is in the thousandths of an inch range, it results in press fatigue and die misalignment.
One known press construction attempts to eliminate the problems caused by the flexing of the die-holding lower bed and resulting inward stresses which are placed on the side frame members by transmitting the bed loads to the frame through large-diameter, circular bearing blocks. This construction consists of a pair of spaced key-shaped bearing members which are rigidly mounted on the front ends of the side frames. These bearing members project into complementary-shaped keyway openings formed in the vertical front plate of the bed. This mounting arrangement enables the bed during flexing to rotate on the circular portion of the key-shaped bearing members. However, this arrangement does not enable the bed plate to rotate on the key-shaped bearings about a common axis which extends horizontally between the center points of the bearings to compensate for the twisting and skewing forces exerted on the top die and ram to prevent misalignment of the mating dies.
Accordingly, the need has existed for a gap-framed or C-type press which eliminates or substantially reduces misalignment between the upper and lower dies which heretofore occurred due to the unbalanced forces which are exerted on the C-shaped press frame during a press operation. There is no known gap-framed or C-type press construction of which we are aware which eliminates this problem by the mounting of the press bed and side frames on a pair of spherical bearing members.